The present invention relates to the field of anti-inflammatory substances and other substances which act by inhibiting binding to the intracellular domain of a tumor necrosis factor receptor (hereinafter "TNF-R"), such as, for example, the P55 type (or TNF-R1) TNF receptor. More particularly, the present invention is directed to novel ligands which bind to the TNF-R intracellular domain and to inhibition or modulation of signal transduction by this receptor.
Tumor necrosis factor (herein "TNF") is a cytokine which produces a wide range of cellular activities. TNF causes an inflammatory response, which can be beneficial, such as in mounting an immune response to a pathogen, or when overexpressed can lead to other detrimental effects of inflammation.
The cellular effects of TNF are initiated by the binding of TNF to its receptors (TNF-Rs) on the surface of target cells. The isolation of polynucleotides encoding TNF-Rs and variant forms of such receptors has been described in European patent publication Nos. EP 308,378, EP 393,438, EP 433,900, EP 526,905 and EP 568,925; in PCT patent publication Nos. WO91/03553 and WO93/19777; and by Schall et al., Cell 61:361-370 (1990) (disclosing the P55 type TNF receptor). Processes for purification of TNF-Rs have also been disclosed in U.S. Pat. No. 5,296,592.
Native TNF-Rs are characterized by distinct extracellular, transmembrane and intracellular domains. The primary purpose of the extracellular domain is to present a binding site for TNF on the outside of the cell. When TNF is bound to the binding site, a "signal" is transmitted to the inside of the cell through the transmembrane and intracellular domains, indicating that binding has occurred. Transmission or "transduction" of the signal to the inside of the cell occurs by a change in conformation of the transmembrane and/or intracellular domains of the receptor. This signal is "received" by the binding of proteins and other-molecules to the intracellular domain of the receptor, resulting in the effects seen upon TNF stimulation. Two distinct TNF receptors of .about.55 kd ("TNF-R1") and .about.75 kd ("TNF-R2") have been identified. Numerous studies with anti-TNF receptor antibodies have demonstrated that TNF-R1 is the receptor which signals the majority of the pleiotropic activities of TNF. Recently, the domain required for signaling cytotoxicity and other TNF-mediated responses has been mapped to the .about.80 amino acid near the C-terminus of TNF-R1. This domain is therefore termed the "death domain" (hereinafter referred to as "TNF-R death domain" and "TNF-R1-DD") (see, Tartaglia el al., Cell 74:845-853 (1993)).
While TNF binding by TNF-Rs results in beneficial cellular effects, it is often desirable to prevent or deter TNF binding from causing other detrimental cellular effects. Although substantial effort has been expended investigating inhibition of TNF binding to the extracellular domain of TNF-Rs, examination of binding of proteins and other molecules to the intracellular domain of TNF-Rs has received much less attention.
However, ligands which bind to the TNF-R intracellular domain have yet to be identified. It would be desirable to identify and isolate such ligands to examine their effects upon TNF-R signal transduction and their use as therapeutic agents for treatment of TNF-induced conditions. Furthermore, identification of such ligands would provide a means for screening for inhibitors of TNF-R/intracellular ligand binding, which will also be useful as anti-inflammatory agents.